1. Field of the Invention
The present invention relates to a fuel evaporative emission control device, specifically control of operation of the fuel evaporative emission control device.
2. Description of the Related Art
In a prior-art technique to prevent fuel evaporative gas, produced within a fuel tank, from being emitted to the atmosphere, a fuel tank shutoff valve (sealing valve) is fitted to a passage connecting a fuel tank to a canister to seal the fuel tank, and at the time of filling the fuel tank, the sealing valve is opened to allow fuel evaporative gas to flow from the fuel tank into the canister and become adsorbed within the canister.
When the fuel tank is sealed by the sealing valve as in the aforementioned system, an increase in ambient air temperature may lead to a high pressure in the fuel tank because of more fuel evaporating within the fuel tank, which may lead to fuel evaporative gas being emitted to the atmosphere at the time of filling the fuel tank.
To prevent fuel evaporative gas from being emitted to the atmosphere at the time of filling the fuel tank, the sealing valve is opened upon detecting filling operations, and opening the fuel tank is inhibited until the pressure in the fuel tank decreases to a sufficiently low level.
However, it takes long for the pressure in the fuel tank to decrease to a desired level, and thus, it takes long before filling can be started.
To cope with this problem, a technique has been developed in which when the pressure in the fuel tank increases, if the engine is running and purge is being conducted, the sealing valve is opened to emit high-pressure fuel evaporative gas from the fuel tank into the intake passage of the engine, without letting them be adsorbed in the canister, thereby reducing the pressure in the fuel tank (JP 4110932 B2).
In the fuel evaporative gas management device in the aforementioned publication, if the pressure in the fuel tank increases to a high level while the engine is running, the sealing valve is opened and high-pressure fuel evaporative gas are directed from the fuel tank to the intake passage, and when the engine stops, the sealing valve is closed and purge is stopped. The manipulations of the sealing valve and the purge actions are thus synchronized.
When the manipulations of the sealing valve and the purge actions are synchronized, and thus, the purge is stopped at the same time that the sealing valve is closed, it follows that highly-concentrated fuel evaporative gas remain in the passage between the sealing valve and a purge control valve provided for control of purge.
If the engine is started and purge is resumed in this situation, the highly-concentrated fuel evaporative gas remaining in the passage is emitted into the intake passage. This is undesirable because it causes variations in air-fuel ratio of the intake air-fuel mixture drawn into the engine, which lead to variations in engine output and worse emissions.